Short term pharmacological immobilization in macaque monkeys.

OBJECTIVE: To develop a safe and effective immobilization protocol in rhesus monkeys, which is not based on dissociative anaesthetic agent. STUDY DESIGN: Prospective, randomised, experimental trial. ANIMALS: Twenty rhesus monkeys, weighing 2.6-8.0 kg, 1-3 years of age, of both sexes. METHODS: The monkeys received 50 µg kg(-1) medetomidine, 0.25 mg kg(-1) midazolam and 5 µg kg(-1) fentanyl with 150 IU hyaluronidase intramuscularly (IM). The animals were closely observed for behavioural changes and reaction to sound stimulus. Pulse rate and oxygen saturation of haemoglobin (SpO(2) ) were monitored every 5 minutes, for 20 minutes. After this period, 250 µg kg(-1) atipamezole or a placebo was administered IM and behavioural changes were closely observed. RESULTS: Full immobilization was observed after mean 269 ± SD 116 seconds. Ten minutes after injection mean arterial oxygen saturation of haemoglobin was 94 ± 4%, but did not fall significantly further. The median pulse rate was 116 beats minute(-1) 5 minutes after the administration of the drug. This level further decreased to a median level of 108 beats minute(-1) 20 minutes after the drug's administration. The median time to recover from immobilization was significantly shorter after atipamezole administration when compared to placebo (2.7 versus 55 minutes). All animals awoke smoothly and no side effects such as vomiting or agitation were observed. CONCLUSIONS: Short term and reversible pharmacological immobilization was achieved using combination of midazolam, medetomidine, and fentanyl. CLINICAL RELEVANCE: The present study demonstrates that 20-minute pharmacological immobilization with a combination of midazolam, medetomidine, and fentanyl is feasible in rhesus monkeys with minimal effect on heart rate.